The present invention relates to a disk apparatus for rotating disk media by a brushless DC motor having no Hall element and, more particularly, to a disk apparatus for always rotating and activating in a specified direction without reversely rotating a motor upon activation.
In recent years, in a magnetic disk apparatus or optical disk apparatus or the like, in order to realize a small size and a high performance of the apparatus, a reduction in number of parts due to an integration of parts used, an exclusion of unnecessary parts, and the like is actively performed. Thus, as for a spindle motor which is used for rotation of the disk media, a high speed, a low electric power consumption, and low costs are being realized.
Hitherto, a brushless DC motor is used as a spindle motor of the disk apparatus. A Hall sensor is used for a speed control and a confirmation of the stop position upon activation of such a brushless DC motor. In case of the brushless DC motor of three-phase windings which is ordinarily used, three Hall sensors are fixedly arranged on the winding side with intervals of 120.degree. or 60.degree., a current supply timing of a coil is controlled on the basis of a detection signal when a rotor magnetic pole passes through each Hall sensor, thereby rotating the motor in the specified direction at a predetermined rotational speed.
Due to the miniaturization and the realization of the high performance of the apparatus, however, the use of a brushless DC motor having no Hall sensor has begun. According to such a DC motor, since it is unnecessary to assemble the Hall sensor in the motor, the motor can be miniaturized by the space of such a Hall sensor. Since an assembling space of the Hall sensor can be used to install a stator coil, the torque can be increased.
As for a rotation control of the brushless DC motor having no Hall sensor, a counter electromotive force which is generated in the coil by the motor rotation is detected and the current supply timing of the coil is controlled on the basis of the counter electromotive force detection signal, thereby rotating the motor in the specified direction at a predetermined rotational speed. On the other hand, in an activation control, first, a pulse current is supplied to a specific coil phase. When the rotor stops in a dead zone of the stator coil, the motor cannot be activated. In order to avoid such a situation, however, the position of the rotor is again decided by a pulse driving and the rotor is moved out from the dead zone. Subsequently, a synchronous (referred to as a "sync") control is performed until the counter electromotive force detection signal is obtained from the coil. The counter electromotive force detection signal is made valid after the motor rotational speed rises to about 1000 to 2000 r.p.m. Since there is no timing signal serving as a reference for a period of time of a low rotational speed so far, the sync control for switching the current supply to the coil at a timing synchronized with a pulse having a specific frequency obtained from a clock pulse is executed. When the rotational speed rises and the counter electromotive force detection signal is made valid during the sync control, the current supply to the coil is switched at the timing based on the counter electromotive force detection signal, thereby leading the rotation. When the rotational speed reaches a specified rotational speed of, for example, 5400 r.p.m., a speed lock-on (notification of the completion of the activation) is raised, thereby starting a control mode of a stationary rotation.
In order to rotate the motor in the specified direction from the stop state of the motor, the stop position of the motor has to be known. However, the counter electromotive force of the coil becomes a signal having a level that can be used in the timing control only when the motor rotational speed exceeds, for example, 1000 r.p.m. Consequently, the stop position cannot be confirmed by the detection signal of the counter electromotive force and the rotating direction of the motor cannot be decided upon activation.
According to the conventional activation control, since the stop position of the rotor for the coil is not known, the current supply to the coil is started in accordance with the order which has fixedly been decided. There is, accordingly, a case where the motor reversely rotates depending on the stop position of the rotor although it doesn't happen every activation. In case of a three-phase and two-pole brushless DC motor in which the rotor has only the S and N poles, a probability of such a reverse rotation is equal to 1/2. When the spindle motor reversely rotates, according to the circumstances, there is a case where the heads and the disk media are damaged. In case of a large damage, it causes a serious damage such as a loss of internal data or the like. Although a countermeasure for reduction of the damage for the reverse rotation of the spindle motor has been taken for the heads and disk media, such a countermeasure is not always perfect. In order to increase degrees of freedom of the heads, disk media, and housing structure, the activation control of the spindle motor which doesn't cause a reverse rotation is necessary.